1. Field of the Invention
The present invention relates to a display control system which displays multiple areas on a display screen and which displays picture signals from different signal sources in the respective areas, and to a display control method.
2. Description of the Related Art
Heretofore, advances in communication technology have led to advances in networking in the office place, such that various types of equipment are connected to personal computers, with the functions thereof being shared. In recent years, standardization for communications between home appliances, such as HAVi or Jini, has advanced with interfaces such as IEEE1394 and USB, and, accordingly, networking of equipment within the home is also advancing.
On the other hand, television sets and personal computer displays had been entirely separate entities, but these have merged to where there are television sets capable of displaying personal computer screens, and personal computer displays capable of inputting television signals.
Further, with wide-screen televisions, plasma displays, rear-projection televisions, projectors, and other like large-screen display devices, there are increasingly more opportunities in both office and home for use associated with various picture sources, such as for movies, television, home videos, presentations, tele-conferencing, displaying various types of information, and so forth. As such, there is demand for display devices to have multi-screen display functions wherein one screen is divided into multiple screens for displaying images of different image signal sources.
FIG. 13 is a block diagram illustrating a configuration of a display device for a personal computer, as an example of a commonly-used conventional display device. In the figure, reference numeral 301 denotes a personal computer serving as an image signal source. Reference numeral 315 denotes a personal computer display device serving as a display device. Here, a display device for sending image signals as digital data is shown.
Looking at the image signal source 301, reference numeral 302 denotes a CPU (Central Processing Unit), 303 denotes a bus control unit for sending control signals from the CPU 302 to components of the image signal source 301, 311a is a system bus line made up of a data bus and control bus connecting the components, and 311b denotes a bus line between the CPU 302 and the bus control unit 303.
Reference numeral 304 denotes a main memory, 305 denotes a recording medium such as a hard disk or the like, and 306 denotes a graphics drawing unit for creating image signals for display, which are output according to output image attributes (resolution, pixel frequency, screen refresh frequency, gamma properties, gradients, color properties, etc.) for the display device 315.
Reference numeral 307 denotes image memory used by the graphics drawing unit 306 when processing images, 311e denotes a data bus and a control bus between the graphics drawing unit 306 and the image memory 307, and 308 denotes an image transmitting unit for sending image signals created by the graphics drawing unit 306 to the display device 315. Specifically, this is a TMDS sending device using DVI (Digital Video Interface) standards established by DDWG (Digital Display Working Group) which is a display device standardization group, or a sending device that compresses images or only sends partially rewritten portions.
Reference numerals 309 and 310 denote portions for performing communication between the display device 315 and the image signal source 301 (personal computer). Here, there is a standard for communication between display devices and personal computers, called DDC (Display Data Channel) communication. DDC is a standard for performing an exchange such that a computer can recognize and control a display device, and is recommended by VESA (Video Electronic Standard Association), which is a display-related standardization group.
Based on this communication method, EDID (Extended Display Identification Data) format (also standardized by VESA) display attributes information is sent from the display device side to the personal computer side. This was issued as a standard in Extended Display Identification Data Standard version 3 (Revision Date: Nov. 13, 1997).
The DVI standards also use this DDC communication to perform communication between display devices and personal computers, and also specifies hot-plug functions (functions for detecting connection with a personal computer and performing DDC communication). Reference numeral 310 denotes a DDC communication unit for performing this DDC communication, and 309 denotes a connection detecting unit for realizing the hot-plug functions.
The connection detecting unit 309 is connected to the ground or the power source through resistance when not connected to the display device 315, for example, and connection thereof causes the ground potential or power source potential to change, thereby detecting connection of a display. Reference numeral 311c denotes a line group for sending signals from the connection detecting unit 309 and the DDC communication unit 310 to the graphics drawing unit 306. Control between the connection detection unit 309 and the DDC communicating unit 310 is controlled by the CPU 302.
In at the display device 315, reference numeral 317 denotes a micro-computer unit for controlling the display device. Reference numeral 325a denotes a line group made up of a control bus from the micro-computer unit 317, 318 denotes an image receiving unit for receiving picture images such as TMDS standard signals or the like sent from the image transmitting unit 308 and for converting the signals into a format suitable for signal processing, such as RGB 8-bit signals, and 319 denotes a resolution converting unit for performing a conversion, such as resolution conversion or image-refreshing frequency conversion, for matching the number of pixels of the image from the image signal source 301 (personal computer) to the display pixel number of the display device 315.
Reference numeral 320 denotes an image memory, 325e denotes a data bus and a control bus for the image memory, and 321 denotes an image display processing unit for converting gamma properties, color properties, etc., to match the properties of a liquid crystal or CRT image display unit, and for performing text display such as on-screen display. Reference numeral 322 denotes an image display unit made up of devices such as liquid crystal, CRT, PDP, EL, LED, or the like.
Reference numeral 324 denotes a DDC communication unit for performing DDC communication, 323 denotes a connection signal supplying unit for supplying a bias voltage or the like for providing a signal indicating that a connection has been made, and 325b through 325d are data buses for image signals.
Reference numerals 314a through 314c denote lines connecting the image signal source 301 (personal computer) and the display device 315, 314a is a line for image signals, 314b is a line for DDC communication, and 314c is a line for connection detection. Normally, 314a through 314c are batched as one dedicated image cable.
As shown in this example, conventional display devices for personal computers are connected to a personal computer for inputting the image on a one-to-one basis. The resolution of a displayed image accordingly is determined by transferring EDID data by DDC communication when starting up the image signal source 301 (personal computer) or performing connection detection of the display device 315.
Methods known for the image output device to obtain information on the display device include conventional exchange of EDID data by DDC communication (currently Ver. 3.0) and the HAVi (Home Audio/Video Interoperability) standard (currently Ver. 1.0), but both of these only assume communication of full display-area information (number of display pixels, aspect ratio, MPEG compression format transfer, and so forth).
Accordingly, when transferring multiple picture signals to an arbitrary screen display area of the display device, output from picture signal sources must be sent as the same signal as for the entire display area, even when the display device is a picture-in-picture display device. This risks exceeding the upper limit of the amount of information a transfer path can carry of picture signals.
Also, with DDC communication, the EDID information is one-way from the display device to the signal source, and due to the fact that the display device cannot accurately grasp the resolution of image signals to be input, and that the time for performing communication is limited to the time of starting up the personal computer or the time of physically connecting the display device and the signal source, there is no way to perform communications for changing image attributes (display area and resolution, compression percentage, sending format, etc.) and audio information or controlling the amount of information (selection information, stopping, starting, changing compression percentage, etc.), while displaying an image.
Further, simply obtaining the picture signals, which the signal source itself outputs, makes the amount of image information for multiple signals sources mutually unclear. Therefore, even in cases where there is the problem in which the total amount of image signal data being input to the input system of a display device exceeds its capacity, detection of the problem and reduction in the amount of information by mutual control cannot be performed.
Japanese Patent Laid-Open No. 10-234020 discloses a communication method for reducing the amount of data transferred at the sending side, when exchanging images among multiple devices, but the method assumes specialized exchange devices and is not capable of managing the amount of image information in environments wherein different devices have been connected.
FIG. 14 is a block diagram illustrating a connection form of various pieces of equipment according to a home appliance communication standard such as HAVi or Jini, which are currently in the processes of standardization. In the figure, reference numerals 401 and 413 denote digital televisions (DTV_A and DTV_B) capable of receiving digital broadcast. Now, the digital television 401 is connected to a network interface, such as IEEE1394, via a set-up box 402, and connected to the set-up box 402 via an image-dedicated cable 419, such as a D-terminal cable.
The digital television 413 has an IEEE1394 decoder built in, and accordingly is directly connected to the network. Reference numeral 404 denotes a personal computer (PC_A), 403 denotes a display device thereof (PC Display_A), and 418a denotes a dedicated image cable thereof. The configuration of the PC_A 404, the display device 403, and the dedicated image cable 418a, corresponds to that shown in FIG. 13. Also, in the same manner, reference numeral 410 denotes a personal computer (PC_B), 409 denotes a display device thereof (PC Display_B), and 418b denotes a dedicated image cable thereof.
Now, the PC_A 404 and the PC_B 410 are connected to the IEEE1394 network, which is not used for sending image signals to the display device, but instead is used for sending other signals.
Reference numeral 405 denotes a digital television tuner (DTV TUNER) of a different system, 406 denotes a digital video (DV), 411 denotes a DVD disk player (DVD), and 412 denotes a server comprised of a hard disk drive (HDD) for recording programs.
These audio-visual devices are connected to the IEEE1394 network, and thus exchange image information. Reference numeral 414 denotes a modem connected to a public network, 416 denotes a telephone line or the like connected to the public network, 407 and 408 denote hubs for dividing and connecting IEEE1394 signals, and 417a and 417j denote IEEE1394 standard communication lines.
With in-home networks thus connected, the user can realize an environment wherein various sources (DTV TUNER, DV, DVD, and HDD)can be operated remotely from the televisions 401 and 413.
However, with conventional in-home networks, a personal computer is connected to a dedicated display in a one-on-one manner, and accordingly personal computer images cannot be referenced via the network by a digital television, as with the other audio-visual equipment.
Also, dedicated cables have been relatively heavy and the sending distance thereof limited, so the personal computer and the display had to be positioned close to one another. This is due to the following reasons.
As a first reason, with a current display device sending method, sending different image signals over the same line results in exceeding the transfer speed limit. For example, in the case of XGA resolution (1024 pixels×768 pixels, 60 Hz refresh cycle, and 65 MHz pixel frequency, 8-bit for each color), the information amount is 1060 Mbit/sec, so the transfer speed of personal computer image signals is greater than the 400 Mbit/sec transfer speed of a IEEE1394 network. Accordingly, there is a need to use dedicated cables for performing specialized sending by TMDS or the like. This data amount can be reduced by performing image compression, but the problem of the excessive information amount on the network remains.
Performing image compression, such as that according to MPEG standards or partial rewriting, may enable a particular piece of information to be sendable as far as the amount of information thereof is concerned, but in the event that this information is to be referenced from an arbitrary location on an in-home network, multiple signals are sent over the same line, so there is the possibility that the transfer speed capacity may be exceeded.
Particularly, in the event of displaying multiple images with a multi-screen display, the number of image signals occupying the line increases, to the extent that the above problem can occur not only for personal computers but also with digital televisions, and digital television arrangements are being developed assuming that signals will be sent over current networks.
As a second reason, the basic concept for determining resolution between current personal computers and display devices assumes a one-on-one arrangement, and does not take into consideration multiple-to-multiple systems unique to networks.
EDID data serving as display attributes information to be transferred from the display device to the personal computer by DDC communication only indicates a list of resolutions of which display can be made, as stated in Extended Display Identification Data Standard Version 3, with the arrangement being such that the actual resolution is selected by the graphics drawing unit of the personal computer that makes reference thereto, and output signals of resolution matching the display device are outputted single-directionally.
Accordingly, displays merely infer from which personal computer signals have been sent by judging the resolution of the sent image signals.
Accordingly, even in the event that there is a problem wherein information signals with large information amounts are sent from multiple information sources, exceeding the processing capacity of the sending line and the display device such that a correct display cannot be carried out, the problem cannot be dealt with from the display device.
Also, the signal source side, such as a personal computer which originally is acting as a host computer, can determine the display capabilities of the display device connected to the signal source, but is not of a configuration to determine the amount of information of other signal sources connected to the display device, and accordingly is not capable of preventing such problems in a system.